To retreive data from the API Profix is working with Swagger. The documentation is available seperately Here.
To check if a method is implemented, you should check the Me functionality. It returns an array with strings called Application Scopes. In the swagger documentation you can find which application scope you should have. This is not a permission scope (Profix API Is not using permission scopes at the moment), but if the underlaying application supports this functionality.
When you are logged in, you should always check which applications are allowed for the logged in user. You can do that with the Applications method. The ID you retreive there, you should use in any other request